Biochar is a carbon sink material with the potential to improve water retention in various soils. However, for the long-term maintenance of green infrastructure, there is an additional need to regulate the water contents in the covers to maintain vegetation growth in semiarid conditions. In this study, biochar-amended soil was combined with subsurface drip irrigation, and the water preservation characteristics of this treatment were investigated through a series of one-dimensional soil column tests. To ascertain the best treatment method specific to semiarid climatic conditions, the test soil was amended with 0%, 1%, 3%, and 5% biochar. Automatic irrigation devices equipped with soil moisture sensors were used to control the subsurface water content with the aim of enhancing vegetation growth. Each soil column test lasted 150 h, during which the volumetric water contents and soil suction data were recorded. The experimental results reveal that the soil specimen amended with 3% biochar is the most water-saving regardless of the time cost. Soil with a higher biochar content (e.g., 5%) consumes a more significant amount of water due to the enhancement of the water-holding capacity. Based on the experimental results, it can be concluded that the appropriate ratio can be determined within 1%-3%, which can reduce not only the amount of irrigated/used water but also the time cost. Such technology can be explored for water content regulation in green infrastructure and the development of barriers for protecting the environment around deep underground waste containment. This study demonstrates a combined technology of biochar and an underground irrigation device for water preservation. Such technology can be also utilized in modifying soil permeability for deep underground barriers for radioactive waste disposal. image Combination of a carbon sink material such as biochar and automated irrigation technology is proposed for regulating soil water content. 1-D column tests were conducted to determine optimal biochar content required for regulating water content within the desired range of field capacity. Water usage is minimal for biochar content between 1% to 3%. This is due to enhancement of soil water retention capacity by biochar. Excess biochar (5% content) can also lead to development of fungi mold on surface of soil and higher water usage.